[torsen] RE: Torsen differential

Keith Maddock Keith.Maddock at trw.com
Tue Nov 19 04:20:38 EST 2002


Sorry, you're missing a major difference between the NVG/Jeep and Haldex/VAG LSC systems.

The NVG/Jeep system is purely mechanical.  I agree that it is not "full time" by the engineering definition, as there is no coupling force without slip.  But the marketing types will refer to this as "full time"

However the Haldex/VAG unit  has more features than that.  It has electronic control of the maximum hydraulic pressure *AND* a small electric motor to maintain a small amount of hydraulic pressure without slip.  Its already there, since 98. The current implementation has a small motor, and open-loop pressure control. 

To quote Haldex: 
"To ensure the function and minimum activation time, the annular pistons are constantly in contact with the rollers via a low pressure maintained by a small electric pump included in the coupling. The pump works only when the vehicle engine is running. With the engine off , the coupling is deactivated, making it possible to tow the vehicle with one axle lifted."

If you dig a little more, you can find some data graphs of their operation.  (Hey they use B+S just like we do!)
Notice that a coupling pressure of 4 bar is always maintained, even at standstill, or when they fully open the throttle valve for a ABS/DSC activation.

The 2nd gen haldex unit is coming soon (its either recently released or in the final stages of development).  We're having one put on our S3, so it will be interesting to compare to the 1st gen unit.    I know the 2nd gen unit adds a pressure sensor to allow them to do closed loop control of the hydraulic pressure (1st gen was open loop and caused inconsistent performance and difficulty in acheiving good control of "partial lock" circumstances)  I'm not sure if the 2nd gen includes a larger electric pump or not, which would allow them to do even more pro-active coupling control.  I'll have to dig into that a bit more.


Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com

>>> David Eaton <deaton at tranzrail.co.nz> 01:28:26 19.11.2002 >>>
thanks for all the explanation keith.  i am quite familiar with the haldex,
and the way that it operates.  it is, by definition, a "hang-on" clutch.  it
can be nothing else as the pressure needed to operate the clutch is
generated by slip in the 1st place.  this is the same whether the
application is jeep or audi.  

if it would help, reference to the nvg site will show that they describe
their 247 haldex lsc-based coupling as "progressive on demand", and not


if it would help further, i can reference an nvg transmission engineer
talking about it.

according to haldex they are developing a variation of the lsc which uses an
external pump to operate the clutch - which obviously fundamentally alters
the use.  this is what may be causing some confusion here.

'95 rs2
'90 ur-q

 -----Original Message-----
From: 	Keith Maddock [mailto:Keith.Maddock at trw.com] 
Sent:	Tuesday, November 19, 2002 12:25 AM
To:	QSHIPQ at aol.com; quattro at audifans.com; Dave.Eaton at clear.net.nz 
Cc:	torsen at audifans.com 
Subject:	[torsen] RE: Torsen differential

Man, this is a rough crowd! :)  While I don't necessarily always agree with
Scott J's comments, some of you guys are making similar non-informed BS
statements that you accuse him of doing.  And please, lets leave personal
attacks off the list.

Warning:  If you are scared of long posts with a lot of information,
(perhaps even more info than is needed to answer the question), hit delete


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